JP2915510B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electrophotographic or electrostatic recording type image forming apparatus, and more particularly, to a method for forming a toner image on an image carrier, and And an image forming apparatus which transfers the toner image onto the recording material by a transfer / separation device and then makes the toner image on the recording material a permanent image by a fixing device, and can be suitably embodied in a color electrophotographic copying machine.

2. Description of the Related Art FIG. 2 shows an example of a conventional color electrophotographic copying apparatus.

According to the color electrophotographic copying apparatus 1a of this embodiment, the photosensitive drum 6 as an image carrier is rotatably supported so as to rotate in the direction of an arrow, and an image forming means is arranged around the photosensitive drum. That is, the photosensitive drum 6 is uniformly charged by the primary charger 7, and is irradiated with a light image that is color-separated by an exposure unit such as a laser beam exposure device or a light image 8 corresponding to the color image. To form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 6 is converted into a visible image, that is, a toner image by the movable developing device 27.

The movable developing device 27 includes four developing devices 27M, 27C, and 27 that separately store four color developers of a magenta color developer, a cyan color developer, a yellow color developer, and a black color developer.
Y, 27BK, and a movable table (not shown) that can hold these four developing units and move in the horizontal direction. The movable developing device 27 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 6, and
The upper electrostatic latent image is developed.

The toner image on the photosensitive drum 6 is transferred to a recording material P which is carried by a transfer / separation device 13 and conveyed in the direction of the arrow in the figure.

Next, the transfer separation device 13 will be described with reference to FIGS.

A transfer drum 30 as a recording material holding unit, which is a part of the transfer separation device 13, has a cylindrical ring 31, which is disposed at both ends,
It is formed of a drum frame 30a constituted by 32 and a connecting portion 33 connecting the cylindrical rings 31 and 32, and a transfer sheet 34 wound around the drum frame 30a. The diameter of the transfer drum 30 is, for example, 160 mm, and the circumferential length is at least twice the width of A4.

The separation means 40, which is a part of the transfer separation device 13, includes a separation claw support 41 provided along the axial direction of the transfer drum 30,
A plurality of, in this example, three, separation claws 42 are fixed to the support 41, and a separation pressing roller 42a is integrally provided at the tip of the separation claw 42. In addition, abutting rollers 45, 46 are applied to both ends of the support 41 via appropriate support plates 43, 44.
Is provided. When the separation claw operation clutch (not shown) is operated, the abutting rollers 45, 46 abut against the cylindrical rings 31, 32 of the transfer drum 30, and guide grooves 35, 32 formed in the rings 31, 32. Guided by 36, the tip of the separation claw 42 is rotated downward, that is, in the normal direction of the transfer drum 30.

A notch 37 is formed in the connecting portion 33 so that the separation claw 42 can be easily inserted between the transfer sheet 34 and the transfer material P sucked and held by the transfer sheet 34. The leading end has a cut 34a along the notch 37 of the connecting portion 33 to the non-image area of the transfer material, and is connected so that the curvature of the transfer sheet 34 (hatched portion in FIG. 5) becomes locally large. Is fixed to the part.

The recording material P is fed by a registration roller 28 in synchronization with the image, as shown in FIG. A transfer material suction unit is provided for holding the transfer material P fed to the transfer device 30 on the transfer sheet by suction. The transfer material adsorption means is
A suction corona charger 23 which is provided inside the transfer drum 30 and applies a charge having a polarity opposite to that of the toner image on the photosensitive drum 6 to the back surface of the transfer sheet 34; and a conductive roller 24 provided outside the transfer drum 30 And The conductive roller 24 is grounded, becomes an opposite electrode of the suction corona charger 23, injects a charge into the recording material P, and transfers the recording material P to the transfer sheet 34.
Has the effect of electrostatically adsorbing. When the conductive roller 24 is attracted, for example, the gap between the conductive roller 24 and the transfer sheet 34 is 0 to 100 μm.
It is arranged so that it becomes. Preferably, the recording material P
Is supplied so that the leading end of the recording material P overlaps the cut 34a of the transfer sheet 34 and does not enter the image area.

When continuous copying is designated by an operation panel (not shown), if the length of the recording material in the transport direction is less than half the length of the peripheral length of the transfer drum 30 minus the width of the connecting portion, The second recording material is fed following the first recording material, and the second recording material is attracted to the transfer sheet 34 at a position symmetrical to the first recording material. That is, two recording materials are simultaneously attracted to the transfer sheet 34 and conveyed. As a result, a copying speed approximately twice as high as when a copying operation is performed without adsorbing only one transfer sheet 34 is obtained.

To transfer the developer of the first color, for example, magenta toner, on the photosensitive drum to the first recording material, a charge having a polarity opposite to that of the toner is applied to the back surface of the transfer sheet 34 using the transfer corona charger 14. . Subsequently, the same latent image is formed again, the first color toner is developed on the photosensitive drum 6, and the first color toner is similarly transferred to the second recording material. By the time the first recording material reaches the position of the conductive roller 24 for the second time, the conductive roller 24 is released, and is separated from the transfer sheet 34 by a distance of 2 mm or more from a position where the transferred toner image is not disturbed. The transfer corona charger 14 transfers the second color toner image (here, cyan) on the photosensitive drum formed in synchronization with the first recording material to which the first color toner has been transferred. Transcribe.

Similarly, the second color toner image is transferred to the second recording material. Similarly, four color toners are transferred to two recording materials. After the transfer step, the charge is removed by using a pair of AC corona dischargers 15 and 16 opposed to each other with the transfer sheet 34 interposed therebetween in order to weaken the attraction force of the recording material to the transfer sheet 34.

In order to separate the first recording material from the transfer sheet 34, a separation claw guided by grooves 35 and 36 of the ring shown in FIG.
The driven outer separation pressing roller 42a integrated with 42
Is pressed against the transfer sheet 34, the outer separation pressing roller 42a moves along the cutout 34a of the connection portion, and the first sheet is recorded where the curvature of the transfer sheet 34 is extremely reduced. A separation claw 42 enters between the leading end of the material and the transfer sheet 34, and the recording material is separated from the transfer sheet 34. When the second recording material is separated from the transfer sheet 34, the inner separation pressing roller 53 that is driven as shown in FIG. 6 is pressed against the transfer sheet 34, and the outer separation pressing roller 42a is also a ring. Guided by a groove provided on the opposite side of the upper connecting part,
The transfer sheet 34 is pressed against the transfer sheet, and the curvature of the transfer sheet 34 is locally reduced, the leading end of the recording material is separated by curvature, and the separation is performed by inserting a separation claw 42 between the recording material P and the transfer sheet 34. In order to prevent image disturbance due to peeling discharge that occurs when the recording material and the transfer sheet are separated, it is preferable to perform an AC corona discharge using the corona discharger 17.

If the length of the recording material in the transport direction is longer than that described above, the leading end of the recording material is attracted to the transfer sheet 34 at the same position as the leading end of the first recording material regardless of whether one copy or continuous copying is performed. First, a transfer / separation process similar to that for the first recording material is performed. At this time, the inner separation pressing roller is not driven. After the transfer / separation process, the recording material passes through the conveyor belt 25,
The sheet is sent to the fixing device 26. The fixing device 26 will be described with reference to FIG.

The fixing device 26 includes a fixing roller 121 and a pressure roller 125. The two rollers 121 and 125 are pressed against each other and driven to rotate in the direction of the arrow. The fixing roller 121 is made of an aluminum core 1
HTV silicone rubber (high temperature vulcanization type silicone rubber) 123 is coated to a predetermined thickness on the outer layer 22 and L is further coated on the outer layer.
TV silicone rubber (low temperature vulcanization type silicone rubber) 12
4 is coated to a thickness of 200 μm. The pressure roller 125 is formed by coating an outer layer of an aluminum core bar 126 with HTV silicone rubber 127 to a predetermined thickness, and further coating a surface layer thereof with a resin film 127 ′. The fixing roller 121
And a halogen heater 1 as a heating source in the pressure roller 125.
28 are provided respectively. Then, a thermistor 129 is brought into contact with the pressing roller 125, and the turning on / off of the current supply to the halogen heater 128 is controlled by the thermistor 129. In this way, the surface temperatures of the fixing roller 121 and the pressing roller 125 are maintained at a predetermined value (for example, 170 ° C.) suitable for fixing the unfixed toner image on the recording material P on the recording material P. It has become.

On the other hand, in order to improve the releasability of the toner from the fixing roller 121, the release agent
Two are provided. The release agent coating device 132 is provided with a silicone oil 133 (Shin-Etsu Chemical Co., Ltd.) in an oil tank 132a.
Dimethyl silicone oil KF96 300CS) roller group 1
After being pumped up by 34 and 135, the pumped up silicone oil 133 is regulated to a fixed amount by an application amount adjusting blade 140, and then the silicone oil 133 is fixed to the fixing roller 121 by an on / off device comprising a plunger 142 and a spring 143.
Apply to.

The recording material P is passed between the fixing roller 121 and the pressure roller 125 having the above configuration, so that the toner image is fixed on the recording material P by the heat and pressure of the roller.

A developer used in such a color electrophotographic copying apparatus, that is, a toner will be described.

In forming a multi-color image or a full-color image, by using a sharp-melt toner, the color reproduction range of a copy can be widened and a color copy faithful to the original can be obtained satisfactorily.

The toner is formed by melting and kneading a binder resin such as a polyester resin or a styrene-acryl ester resin, a toner forming material such as a colorant (dye, sublimable dye), and a charge control agent.
It is manufactured by crushing and classifying. If necessary,
Various external additives (for example, hydrophobic colloidal silica) are added to the toner.

In consideration of fixability and sharp meltability, a color toner using a polyester resin as the binder resin is particularly preferable. Examples of the sharp melt polyester resin include a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid.

In particular, (Wherein R is an ethylene or propylene group, X and Y are each a positive integer of 1 or more, and the average value of X + Y is 2 to 10) or a substituted derivative thereof. A diol component, a divalent or higher carboxylic acid, an acid anhydride thereof or a lower alkyl esterified carboxylic acid (eg, fumaric acid, maleic acid, maleic anhydride, phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) ) Is a polyester resin obtained by at least co-condensation polymerization with a dicarboxylic acid, because it has sharp melting characteristics. The softening point of the polyester resin is 75 to 150 ° C, preferably 80 to 120 ° C. FIG. 8 shows the softening characteristics of a toner containing a polyester resin as a binder resin.

To explain the method of measuring the softening point, the flow tester
Using a CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) having a diameter of 0.2 mm and a thickness of 1.0 mm was applied with an extrusion load of 20 kg, and the initial setting temperature was 70 ° C, and after a preheating time of 300 seconds, 6 ° C.
When the temperature is raised at a constant speed at a rate of / min, a plunger drop amount-temperature curve (softening S-shaped curve) of the drawn toner is obtained. The toner used as the sample is a fine powder weighed accurately by 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm ² . The softening S-shaped curve is as shown in FIG. As the temperature rises at a constant speed, the toner is gradually heated and starts flowing out (plunger descent A-
B). When the temperature is further increased, the toner in a molten state flows out greatly (BCD), the plunger descent stops, and the process ends (DE).

The height H of the S-shaped curve indicates the total outflow, and the temperature T ₀ corresponding to the point C of H / 2 indicates the softening point of the sample (for example, toner or resin).

Whether or not the toner and the binder resin have sharp meltability can be determined by measuring the apparent melt viscosity of the toner or the binder resin.

With toner or binder resin having sharp melt property,
The temperature at which the apparent melt viscosity shows 10 ³ poises is T ₁ , 5
× 10 ² poise T ₁ = 90 to 150 ° C. When the temperature was T ₂ of the case showing the _{| ΔT | = | T 1 -T} 2 | = 5~20 refers to satisfy the condition of ° C..

A sharp-melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity is reduced extremely sharply when heated. Such a decrease in viscosity causes appropriate mixing of the uppermost toner layer and the lowermost toner layer, and at the same time, sharply increases the transparency of the toner layer itself, thereby enabling good subtractive color mixing.

Problems to be Solved by the Invention However, the image forming apparatus has the following problems.

That is, in the past, paper was generally used as a recording material, and in particular, a material of about 50 to 90 gm ² was often used.
However, in accordance with recent various needs, more types of recording materials are desired, and thick papers such as 90 to 150 gm ² , recording materials using resinous films, and the like may be used. Especially the latter
Many are used as OHP films (films for overhead projectors). When such a recording material is used, it is necessary to fix the image at a lower speed than usual, unlike the related art, when fixing the image.

For example, in the case of this example, the process speed of the main body is 84 mm / s
When it is ec, the fixing speed is usually 84 mm / sec,
The fixing speed when fixing at a low speed is 25 mm / sec. This fixing speed (84 mm / sec) is not sufficient, for example, when fixing on thick paper. The amount of heat for melting the toner is insufficient, and the gloss of the image after fixing is lost, or the recording material and the toner are stuck together. There is no so-called "cold offset", which is particularly likely to occur in a color image forming apparatus. That is, this is because the toner from the fixing roller side is hardly transmitted to the lowermost layer because the toner is thickened in two to four layers on the recording material, and the lowermost layer toner is hardly melted. Because the heat from the back surface does not easily reach the toner in the lowermost layer through the paper, the toner in the lowermost layer hardly melts, the toner does not have an anchor effect on the paper, and the toner peels off from the paper. It is.

Further, when the recording material is a resinous film, it is difficult for heat to be transmitted as in the case of thick paper, and further, since the film surface has good smoothness, the toner anchor effect cannot be obtained.
Since the paper is peeled, it is necessary to fix the paper at a low speed as in the case of thick paper.

Also, in the case of an OHP film, in order to obtain color development and light transmittance of an image, and further to improve color development of a color toner when projected, fix the toner at a low speed and melt and mix the toner. It is necessary to fix well together.

When the fixing device 26 having the above configuration is used, the transfer separation device 13
When two recording materials are adsorbed and transferred on top and separated,
The two recording materials transported by the transport belt 25 are used as a fixing device.
When the fixing device 26 performs fixing at a low speed when passing through the second recording material 26, the second recording material catches up with the first recording material being fixed, and Image was disturbed or a paper jam occurred.

In order to prevent such a situation, when the fixing speed is reduced and the transport speed of the transport belt 25 is also reduced at the same time, the transport belt 25 is configured not to be long enough to carry two transfer materials. In the case of a copier,
The second recording material forms a loop in the vicinity of the separation claw 42, contacts the static elimination corona discharger 17, etc., and disturbs the image,
Paper jams may occur.

Accordingly, an object of the present invention is to make the interval of entry of the recording material into the fixing device variable according to the required fixing speed of the recording material, thereby preventing the occurrence of image disturbance on the recording material and clogging of the recording material. Another object of the present invention is to provide an image forming apparatus capable of always obtaining a permanent image of stable image quality.

Means for Solving the Problems The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier on which an unfixed toner image is formed, a recording material carrying means for carrying a recording material, and a device capable of conveying the recording material at a first speed or a second speed lower than the first speed. Fixing means, and the unfixed toner image formed on the image carrier is transferred onto a recording material carried on the recording material carrying means, and the recording material on which the unfixed toner image is transferred is In an image forming apparatus in which an unfixed toner image is fixed on a recording material by being conveyed by the fixing unit after being separated from the recording material holding unit, regardless of the first speed and the second speed selected by the fixing unit, The recording material carrying means can simultaneously carry the first recording material and the second recording material and can transfer an unfixed toner image to the second recording material subsequent to the first recording material. Material and the second recording material are carried, and the unfixed toner is The time from when the image is transferred to when the second recording material enters the fixing means is longer when the second speed is selected than when the first speed of the fixing means is selected. The image forming apparatus is a feature.

Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows an embodiment of the image forming apparatus according to the present invention. In the color electrophotographic copying apparatus described with reference to FIG. 2, a transport belt 25 is a front transport belt 25A and a rear transport belt 25B. , And the other configurations and functions are the same. Therefore, components having the same configuration and function are denoted by the same reference numerals, and detailed description is omitted.

Therefore, in the present embodiment, as in the case of the above-mentioned conventional apparatus, when a plurality of copies are made, two recording materials P can be simultaneously attracted to the transfer / separation device 13, and the toner of each color is deposited on the recording materials P. After that, the recording material P is separated from the transfer drum 30.

Of the two recording materials continuously separated from the transfer / separation device 13, the recording material separated first is conveyed from the subsequent conveyance belt 25B to the previous conveyance belt 25A, and the separated recording material is subsequently conveyed. The material rides on the later transport belt 25B.

In the present invention, as a recording material, when thick paper or a resinous film or the like, which must be fixed at a lower speed than usual, is used, the recording material separated first rides on the front conveyance belt 25A, and subsequently, When the separated recording material rides on the rear conveyance belt 25B, the rear conveyance belt 25B is stopped, and only the front conveyance belt 25A is operated. As a result, only the previously separated recording material is fixed at a low speed by the fixing device 26, and after the previous recording material is discharged, the rear conveyance belt 25B is operated, and the recording material on the conveyance belt is moved to the front conveyance belt. 25A
, And further conveyed to a fixing device where the toner is similarly fixed at a low speed and discharged.

As described above, in the present embodiment, the interval at which the recording material enters the fixing device 26 is made variable according to the fixing speed, and the time from when the toner is transferred to the subsequent recording material to when the recording material enters the fixing device 26 is changed. The time is longer when fixing is performed at a lower speed than when the fixing is performed at a normal speed.

With the above configuration, it is prevented that the second recording material catches up with the first recording material in the fixing device or the like, and good image formation can be performed without causing image disorder or paper jam.

As described above, the present invention is not necessarily limited to two transport belts.
25A and 25B are not required, and the present invention can also be realized in an image forming apparatus having a single transport belt 25 as shown in FIG.

In the present embodiment, when the copying is set to a plurality of sheets, the recording material is continuously fed, the two recording materials P are simultaneously attracted onto the transfer / separation device 13, and the toner of each color is deposited on the recording material. When transferred and then separated, the two recording materials P on the transfer / separation device 13 are not continuously separated. First, only one recording material P is separated by the separation / separation device 13 by the separation means 40.
Separated from Other recording materials are left on the transfer / separation device 13 without being separated, and subsequently rotate together with the transfer drum 30.

That is, the recording material P closer to the connecting portion 33 of the transfer drum 30
Is separated, and the subsequent recording material P is continuously rotated while remaining on the transfer separation device 13.

The first separated recording material is conveyed to the fixing device 26 via the transport belt 25, and is fixed at a low speed.

Next, after the fixing of the first recording material is completed, the second recording material is separated, similarly conveyed to the fixing device 26 via the transport belt 25, and fixed at a low speed.

With the above configuration, the second recording material does not catch up with the first recording material in the fixing device 26 or the like, and good image formation without image disturbance, paper jam, and the like can be performed.

In the above embodiment, the recording material to be separated first is the first recording material close to the connecting portion 33. However, after the recording material is continuous, that is, the second recording material is separated first. You may. However, from the viewpoint of the continuity of the image forming operation,
It is preferable that the recording material be separated from the recording material closer to the connecting portion 33.

After the first recording material is separated, the transfer separation device 13
The other recording material remaining on the surface is still rotating on the transfer / separation device. At this time, the transfer corona charger 14 should be slightly operated (charging operation).

That is, since a plurality of layers of toner images are formed on the second recording material suction-held on the transfer drum 30, the photosensitive drum 6 and the photosensitive drum 6 are rotated on the transfer separation device 13. This is to prevent the toner image from being disturbed by the contact of the recording medium and the recording material from being peeled off from the transfer / separation device 13.

In this embodiment, the timing for separating the second recording material from the transfer / separation device 13 is as follows: (a) After the first recording material is fixed at a low speed and the fixing operation is completed, The second recording material is separated from the transfer separation device 13.

(B) While the first recording material is fixed at a low speed,
The timing at which the first recording material is separated and enters the fixing device for the second recording material may be any time as long as the first recording material has been fixed.

Such a method is preferably used.

In the present invention, the detection that the recording material is a thick paper or a resinous film may be performed by giving an instruction on an operation panel, or on the conveyance path between the registration roller 28 and the conductive roller 24. Thus, it can be automatically detected by an optical sensor or a distance sensor (not shown).

In the case where the image forming apparatus of the present invention is not an image forming apparatus such as a copying machine for giving various instructions from an operation panel as in the present embodiment, but is an apparatus such as a printer which operates according to a signal from a computer. Then, it may be determined that the recording material is a cardboard or a resinous film according to an instruction from the computer.

In each of the embodiments described above, the method of adsorbing the recording material to the transfer / separation device by the attraction force of the electric charge has been described.In addition, two connecting portions 33 are provided on the transfer drum 30 and the recording material is A method of providing a gripper or an air suction hole for holding and holding two recording materials on the transfer drum 30 can also be effectively used in the image forming apparatus of the present invention.

Effect of the Invention As described above, the image forming apparatus according to the present invention has
Regardless of the recording material conveyance speed of the fixing unit, the recording material holding unit can simultaneously hold the first recording material and the second recording material, and can transfer an unfixed toner image to the second recording material subsequent to the first recording material. Therefore, even when the fixing unit conveys the recording material at the second speed, the image forming speed can be improved, and at this time, the unfixed toner image is transferred to the second recording material. Since the time from when the second recording material enters the fixing means is longer when the second speed is selected than when the first speed of the fixing means is selected, the recording material after the previous recording material becomes longer. In this way, it is possible to prevent image disturbance and paper jam from occurring, and to perform favorable image formation.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a conventional image forming apparatus. FIG. 3 is a perspective view of the transfer separation device. FIG. 4 is a perspective view of the transfer drum frame. FIG. 5 is a perspective view illustrating a connecting portion between the connecting portion and the transfer sheet. FIG. 6 is an explanatory diagram for explaining the operation of transfer material separation. FIG. 7 is a schematic configuration diagram of the fixing device. FIG. 8 is a diagram showing the softening characteristics of the toner. 6: Image carrier 13: Transfer separation device 25: Transport belt 25A: Front transport belt 25B: Rear transport belt 30: Transfer drum 40: Separation means

Claims (1)

(57) [Claims] An image carrier on which an unfixed toner image is formed;
An unfixed toner image formed on the image carrier, comprising: a recording material supporting unit for supporting the recording material; and a fixing unit capable of conveying the recording material at a first speed or a second speed lower than the first speed. Is transferred onto a recording material carried by the recording material carrying means, and the recording material on which the unfixed toner image is transferred is separated from the recording material carrying means and then conveyed by the fixing means to be transported by the fixing means. Wherein the fixing member is capable of simultaneously supporting the first recording material and the second recording material irrespective of the first speed and the second speed selected by the fixing device. An unfixed toner image can be transferred to a second recording material subsequent to the first recording material. The first and second recording materials are carried on the recording material carrying means, and the unfixed toner image is carried on the second recording material. From the transfer to the second recording material entering the fixing unit The image forming apparatus is characterized in that the time is longer when the second speed is selected than when the first speed of the fixing unit is selected.